1. Field of the Invention
This invention relates to a flame detecting apparatus and a flame detecting method for detecting a flame through horizontal and vertical scanning for a supervisory region by using a photodetector such as a photodiode or a phototransistor.
2. Prior Art
In a conventional flame detecting apparatus for detecting a flame by allowing a directional flame detector to scan horizontally and vertically within a supervisory region, a pyroelectric element is used as a detecting element of the flame detecting apparatus. The pyroelectric element is generally known as a differential-type detecting element which generates a photo-output only when light energy changes. However, the pyroelectric element is poor in response characteristic to a flame and takes a long time to detect the flame. In addition, the pyroelectric element is expensive, too. By this reason, it may be proposed to use a photodiode or phototransistor which is not expensive and good in response characteristic.
However, the photodiode or phototransistor is not a differential element but a photoelectric transducer element as widely known, which produces an output corresponding to the intensity of light incident thereupon. Therefore, it can not be determined whether there is detected a flame or not, only from a photo-output. A flame can be determined only when a photo-output exceeding a predetermined threshold value, preset for the flame detection determination, is obtained, to produce an alarming output. By this reason, when the photodiode or phototransistor is used as the detecting element of the flame detector, it is liable to be affected by stationary light as ambient phenomena, such as sunlight or light from an incandescent lamp. More particularly, in the case of pyroelectric element, the detecting wave range extends over near infrared range to long wave range, so that the incident light may be passed through a filter so as to detect light which is not present as the stationary light but included in a flame of a fire, for example, to detect emission spectrum of carbon dioxide. On the other hand, since the photodiode or phototransistor has a narrow detecting wave range and it has a best sensitivity in the near infrared range, the detecting range is not set in a non-stationary area even if the incident light is passed through the filter. By this reason, if the sun behind the clouds abruptly appears and shines, or if the sunlight reflected from a mirror in a room is suddenly incident upon the flame detector, the pyroelectric element causes no output. In contrast, the photodiode or phototransistor easily produces a photo-output exceeding the threshold value to give a false alarm.
EPC No. 0098,235 was known as a relative patent in the development of this invention.